Design and Application of Side Channel Spillways

Description: A comprehensive overview of the types, design principles, hydraulic and structural design considerations for side channel spillways in dam infrastructure.

1. Side channel Spillways Design, Function, and Applications Presented by: [AHMED MUSSTAFA] Date: [233724432]

2. Content

3. Introduction Definition: Side spillways are hydraulic structures located on the side of a dam or reservoir used to manage excess water by directing it away from the main structure. Purpose: - To prevent overflow and protect the integrity of the dam. - To safely discharge excess floodwaters. Side spillways are a crucial component of dam infrastructure, playing a vital role in protecting the main dam structure and managing excess water effectively. By diverting surplus water away from the main dam, these spillways help maintain the integrity of the dam and reduce flood risks. Their design, which takes advantage of natural terrain and ease of maintenance, makes side spillways an efficient and economical solution for water management in dams.

4. Background Essential requirements of spillway: 1) it must have adequate discharge capacity. 2) it should be provided with some device for energy decapitation. 3) its discharge should be such that it should not cause flooding on downstream side. 4) it must be safe. 5) its surface must be erosion resistant 6) it should be so located that it should not erode downstream toe of dam. LOCATION: 1) in the body of dam. 2) at one end of the dam 3) away from the body of dam independently. Generally, in gravity dam spillways are provided in body of dam Separate spillway is provided in earthen dam Factor Affecting spillway: Inflow. capacity of out late. Possible damage. Available storage capacity. Gates of spillway. Site condition. Type of dam and its purpose. Height of the crest of spillway. Solid material brought by river its nature and amount. Geological condition. Spillway Layout and Outflow Characteristics Spillway outflow depends on the control device's dimensions and crest level. Maximum discharge and reservoir levels are determined through flood routing. Components are proportioned to match capacity, topography, and foundation conditions, ensuring effective flood management and structural stability.

5. Advantages and Disadvantages Advantages: Protection of the Dam from Flooding : Diverting Excess Water Reducing Pressure on the Dam Efficient Water Management: Controlling Water Levels Providing Additional Flow Paths Utilizing Natural Terrain Design Compatibility with Terrain Ease of Implementation Safety and Maintenance: Ease of Access Enhanced Safety (providing alternative pathways for excess water flow, reducing the likelihood of catastrophic flooding.) Disadvantages: High construction cost. Requires regular maintenance. Potential environmental impact.

6. Types of Spillways Different types of spillways and their functions. Types of Spillways Definition Advantages Uses 1. Ogee Spillway An ogee spillway has a control section shaped like an ogee curve (S-shape), which is ideal for high-velocity water flow.   Efficient in handling high flow rates, good energy dissipation.   Commonly used in gravity dams and arch dams.   2. Side Channel Spillway:   Located on the side of the dam, it directs excess water into a side channel Utilizes natural terrain, provides ease of maintenance.   Used in locations where direct downstream discharge is not feasible.   3. Chute Spillway Water flows down a steeply inclined chute or open channel Handles large volumes of water, good for steep slopes Suitable for dams with large flood discharges.   4. Shaft (Morning Glory) Spillway: Water enters a vertical shaft and is discharged through a horizontal tunnel.   Compact, effective in deep reservoirs.   Used in reservoirs with limited space.   5. Siphon Spillway Uses siphoning action to discharge water once a certain level is reached.   Automatic operation, no moving parts.   Small to medium-sized dams.   6. Labyrinth Spillway:   Features a zigzag crest to increase the effective length of the spillway Increases flow capacity efficiently, good for sites with width constraints.   Enhances discharge capacity without increasing dam height.   7. Duckbill (Fusegate) Spillway:   Modular spillway system that can pivot to release water.   Adjustable, provides additional flood control Allows for controlled release of water during floods

7. Side channel spillway Side channel spillway ➤The flow in this spillway is turned 90° after passing the crest such that the flow is parallel to the weir crest. ➤Best suitable for non rigid dams like earthen dams. ➤It is preferred where space is not available for providing sufficient crest width for chute spillway. ➤The discharge carrier may be an open channel type or a conduit type. Components: Inlet Conveyance channel Control gates Energy dissipator Outlet structure

8. The component parts of a spillway include: These components work together to ensure the safe and efficient management of water flow over the spillway, protecting the integrity of the dam and downstream areas. parts Shapes Function Features Body, Weir, or Spillway   Ogee, U-shaped, semicircular, or circular.   Controls or regulates water flow.   May have gates for flow control Approach Channel Draws excess water from the reservoir to the downstream side.   Admits water into the spillway when the water level exceeds the Full Reservoir Level (FRL), aiding in discharge control.   Energy Dissipators   Reduce the energy of water flowing over the spillway crest to prevent scouring and damage downstream.   Tail Channel Conveys spillway discharge to the downstream side.   Guide Wall Directs water flow from the spillway directly into the downstream river

9. Design Principles of Side Spillways

10. Designing side channel spillways involves careful consideration of hydraulics, structural integrity, and environmental impacts. Here's a simplified outline of the design process: 1. Site Assessment and Data Collection: - Conduct a thorough site assessment to understand the topography, geology, and hydrological characteristics. - Collect data on flow rates, channel geometry, soil types, and any existing infrastructure. 2. Hydraulic Analysis: - Determine the design flow rates and flood frequencies based on hydrological studies and regulatory requirements. - Perform hydraulic analysis to assess the required spillway capacity and flow characteristics. - Consider factors such as velocity, energy dissipation, and potential scouring effects. 3. Spillway Configuration: - Select an appropriate side channel spillway configuration based on site constraints and hydraulic requirements. - Common types include side weir spillways, labyrinth weirs, and side-channel chutes. - Design the spillway structure to safely convey the design flow while minimizing erosion and structural loads. 4. Structural Design: - Design the spillway structure to withstand hydraulic forces, including flow pressure, uplift, and debris impact. - Determine the dimensions, materials, and reinforcement requirements for the spillway walls, floor, and energy dissipation devices. - Consider factors such as foundation stability, construction feasibility, and long-term maintenance. 5. Energy Dissipation: - Incorporate energy dissipation measures to reduce flow velocities and minimize erosion downstream of the spillway. - Options include stilling basins, riprap protection, and flow deflectors to dissipate energy and prevent scouring. 6. Environmental Considerations: - Assess potential environmental impacts of the spillway design, including habitat disruption, sediment transport, and water quality. - Incorporate measures to mitigate impacts on aquatic ecosystems, such as fish passage structures and vegetation restoration. 7. Regulatory Compliance: - Ensure that the spillway design complies with relevant regulatory standards and permitting requirements. - Obtain necessary approvals from regulatory agencies and stakeholders before proceeding with construction. 8. Construction and Monitoring: - Develop detailed construction plans and specifications based on the final spillway design. - Monitor construction activities to ensure compliance with design specifications and environmental safeguards. - Implement a monitoring program to assess the performance of the spillway and address any maintenance or operational issues. Throughout the design process, collaboration with engineers, hydrologists, environmental specialists, and regulatory agencies is essential to ensure a comprehensive and effective solution for side channel spillways.

11. Hydraulic Design Flow Dynamics: Characteristics of Flow over Side Spillways: - Flow over side spillways is characterized by its interaction with the spillway crest and channel geometry. - It exhibits varying velocities, depths, and turbulence depending on factors such as flow rate, spillway design, and hydraulic conditions. - Understanding flow dynamics is crucial for predicting flow behavior, assessing spillway performance, and designing effective hydraulic structures. Calculation of Discharge Capacity: - Discharge capacity of a side spillway is calculated using the discharge formula: Q=C×L×H3/2 Where: - Q is the discharge. - C is the discharge coefficient. - L is the length of the spillway crest. - H is the head over the spillway.

12. Design equations Where: Q: Discharge rate (cubic meters per second, m³/s). (Q=V.A) n: Manning's roughness coefficient (dimensionless), which depends on the surface roughness of the channel. C: is chezy’s coefficient f : is Lacey’s silt factor, which depends on the type of sediment (for non-silty channels, f≈1) A: Cross-sectional area of flow (square meters, m²). R: Hydraulic radius (meters, m), calculated as: R={A}/{P}​ where P is the wetted perimeter (meters, m). S: Channel slope (dimensionless), representing the change in elevation per unit length. Which is v is between the mini v that prevent sedimentation and v max that causes erosion Calculation Steps: Determine Manning's roughness coefficient n : This coefficient depends on the channel roughness. Examples: Smooth concrete channel: n=0.012 Rough earthen channel: n=0.03 Measure the cross-sectional dimensions of the channel : Cross-sectional area A : For example, if the channel is rectangular, the area can be calculated as: A= b×h where b is the width of the channel and h is the water depth. Calculate the wetted perimeter P : Length of the channel in contact with water For a rectangular channel: P=b+2hP = b + 2hP=b+2h Calculate the hydraulic radius The hydraulic radius R is the area divided by the wetted perimeter R : R=A/P​ Determine the channel slope S : This can be measured in the field or obtained from topographic maps. *Final adjustments should be made based on site-specific conditions and additional structural stability checks.   Manning's Equation Lacey’s Equation Chezy’s Equation     Manning's Equation Lacey’s Equation Chezy’s Equation

13. geometric elements of familiar open channel sections

14. Most economical section of open channel A section of a channel is said to be most economical when the cost of the excavation and the lining of the channel is minimum. In other word the wetted perimeter should be minimum for a given discharge. The minimum cross-sectional area and the minimum lining area will reduce the construction cost. The best hydraulic section of an open channel is achieved when it passes maximum discharge for a given cross-sectional area and bed slope. for the maximum discharge or maximum velocity For rectangular cross-sectional B =2 y and the R =y/2 For trapezoidal cross section, the sloping width side should be equal to half of the top width and the hydraulic radius half of thedepth of water. Free board is vertical distance between the design water surface and the top of the channel bank. It is provided to account for uncertainty in design , construction, and operation of the channel. Where y is depth of channel in m (ft) and C is coefficient which varies from 0.7(1.2)for small channels with capacity of 0.6 m 3 /s (20 ft 3 /s) to 0.9 (1.6) for larger channels with acapacityof85m 3 /s (3000 ft 3 /s) or greater

15. Froude No. ( Fr ). It is ratio of inertial force to gravitational force of flowing fluid. provides insight into the flow regime, which can be subcritical, critical, or supercritical, and helps engineers understand the behavior of the flow in the channel. Mathematically, Froude no.is Fr Where v average velocity of flow, y is depth of flow and g is g gravitation acceleration If ; Fr.<1,Flow is subcritical flow The flow is slow and tranquil, dominated by gravitational forces. smooth and controlled flow, reducing the risk of erosion and structural damage. Fr.=1,Flow is critical flow The flow velocity is at a critical point where inertial and gravitational forces are balanced. Fr.>1,Flow is supercritica l flow The flow is fast and rapid, dominated by inertial forces. Requires careful design to manage high energy and potential for flow instability The transition from subcritical to supercritical flow or vice versa can cause hydraulic jumps, which need to be managed to prevent damage. Understanding the flow regime helps in designing energy dissipation structures and selecting appropriate channel dimensions Alternatively: If y> yc , V< Vc Deep Channel Sub-Critical Flow, Tranquil Flow, Slow Flow. And y< yc , V> Vc Shallow Channel Super-Critical Flow, Shooting Flow, Rapid Flow, Fast Flow. Critical depth for rectangular channels : for nonrectangular channels : ( ) Reasons for Achieving Critical Flow Optimal Energy Dissipation Hydraulic Jump Control: At critical flow, the energy in the flow is minimized. Energy Management Maximized Discharge Capacity: Flow Efficiency: Critical flow conditions allow the spillway to handle the maximum operates efficiently during flood events, preventing overtopping Flow Stability: Predictable Behavior: Critical flow provides a stable flow regime, Minimized Turbulence: At critical flow, the flow is neither too slow (which can lead to sediment deposition) nor too fast (which can cause excessive turbulence and erosion) Design Simplification: Simplified Calculations because the relationship between flow depth, velocity, and discharge is well-defined and easier to manage. Standardized Structures:  

16. Hydraulic jump Hydraulic jump is a transition from high-velocity, low-depth (supercritical) to low-velocity, high-depth (subcritical) flow, creating a turbulent zone that dissipates energy. Categorized by the Froude number (Fr), where Fr > 1 indicates supercritical flow, it is calculated using flow depth, velocity, and channel characteristics. This process is essential in managing water flow and preventing erosion in structures like spillways. Effective energy dissipation involves using concrete-lined structures or maintaining subcritical flow with appropriate erosion protection and adequate water depth and basin length

17. Case Studies this hypothetical case, we aim to design a side channel spillway to discharge 100 cubic meters per second (m³/s). We have slope data from GIS showing an average slope of 0.010 for the main channel. For a rectangular shape made of concrete Step 1 : design the shape and the cross section Which is v should be between the mini v that prevent sedimentation and v max that causes erosion Calculation Steps: Determine Manning's roughness coefficient n : Smooth concrete channel: n=0.012 Measure the cross-sectional dimensions of the channel for the maximum discharge : Cross-sectional area A : A= b×y =2y*y. B=2y and R=y/2 So, the equation can be Y=2.5 ,B= 5 Measure the free bord for safty : =0.9+2.5=3.4m total depth The Froude number v 100/2.5*5=8 Fr Energy Dissipation and Flow Regime Ensure energy dissipation structures downstream to prevent erosion, such as a stilling basin or rip-rap. Design an end sill to maintain subcritical flow downstream. Final Design Parameters Width (B) : 10 meters Depth (y) : 3 meters (subject to fine-tuning based on iterations) Concrete-lined spillway : Ensure structural integrity and effective energy dissipation.  

18. Software design steps 1. HEC-RAS Workflow: Set up the Project: Open HEC-RAS and create a new project. Define the river system by inputting the geometry data (river reaches, cross-sections, etc.). Define Flow Data: Enter flow data for different scenarios (steady flow or unsteady flow). Model the Spillway: Add a lateral structure to represent the side spillway. Input the spillway crest profile and weir coefficients. Run the Simulation: Execute the simulation to analyze water surface profiles and spillway flow. Review Results: Review the output tables and graphical profiles to ensure proper design. 2. AutoCAD Civil 3D Workflow: Create the Surface: Import topographic data to create a surface. Design the Spillway Alignment: Draw the alignment for the spillway channel. Create Corridor: Use the alignment and profile to create a corridor model for the spillway. Generate Cross-Sections: Generate cross-sections to review the spillway design. Detailing: Add necessary details such as inlet, outlet structures, and annotation

19. Step 2 modeling :

20. Structural Design of Side Channel Spillways 1. Material Selection: - Concrete: Widely used due to its strength, durability, and ability to form complex shapes. - Reinforced Concrete: Provides additional tensile strength and resilience, making it suitable for high-stress areas and long-term durability. (For a side spillway designed for a dam, reinforced concrete is chosen due to its ability to withstand hydraulic loads and its durability in harsh environmental conditions) 2. Structural Integrity: Load-bearing Capacity: - The structure must withstand hydraulic loads, including water pressure, uplift forces, and potential debris impact. (The spillway is designed to handle a peak discharge of 500 cubic meters per second.) - It should also support its weight and any additional loads during maintenance or extreme events. (Structural analysis ensures the spillway can bear this load without excessive deformation or failure). Durability and Maintenance Considerations: - Durability: Use high-quality materials and proper construction techniques to ensure longevity. with additives to resist sulfate attack and freeze-thaw cycles is used. - Maintenance: Design for ease of inspection and repair, considering access points and modular components for efficient maintenance. (Inspection galleries and access points are included to facilitate regular maintenance and monitoring.) 3. Design Standards: - Relevant Codes and Guidelines: - US Army Corps of Engineers (USACE) Guidelines: Provide comprehensive standards for hydraulic structures, including spillways. - Indian Standards (IS) Codes: Offer specific codes for design and construction of spillways and other hydraulic structures in India. -Other Regional Standards: Follow applicable local or national standards to ensure compliance with regulatory requirements. By selecting appropriate materials, ensuring structural integrity, and adhering to relevant design standards, the side channel spillway is designed to function efficiently, safely, and durably.

21. Analysis of Side Channel Spillway:

22. Construction Details for Side Channel Spillways 1. Joints: Types: Movement and construction joints manage static and dynamic loads. Movement Joints: Accommodate thermal expansion, contraction, and differential settlement. Include water-stops, protected by compressible fillers and sealant. Minimize expansion joints to reduce maintenance issues from high-velocity flow. Contraction joints, preferably with foundation keys and dowels, spaced max 12m on soil foundations and closer on rock foundations. Construction Joints: Continuous reinforcement across joints, avoid vertical joints in slabs. Control joints preferred for moment transfer, reliable water-tightness, and easier construction. High Flow Areas: Avoid joints near baffles, blocks, or sills to prevent pressure-induced damage. 2. Seepage Cut-off Walls: Control seepage flow, velocity, and uplift pressure. Increase seepage path length or tie into less permeable strata. Combine with drainage systems to manage uplift pressure without causing erosion. Typically placed at upstream ends and under transverse joints. 3. Foundation Keys: Prevent differential vertical movement and joint opening. Enhance resistance to sliding on steep slopes. Deep keys used to minimize creep and prevent erosion, especially in energy dissipation structures. Provided at each movement joint on soil foundations and on rock foundations with potential for differential settlement. 4. Water-stops: Prevent water passage and internal erosion at movement joints. Sized to resist at least half the velocity head, full velocity head around energy dissipation features. Installed per manufacturer’s instructions, designed for expected dynamic loads and structural displacements.

23. Environmental and Safety Considerations Environmental Impact: Impact on Local Ecosystems: Habitat Disruption: Construction and operation can disrupt local wildlife habitats, affecting terrestrial and aquatic species. Water Quality: Changes in water flow and sediment transport can alter water quality and aquatic ecosystems. Vegetation: Removal of vegetation during construction can lead to soil erosion and loss of native plant species. Fish Migration: Spillways can obstruct fish migration paths, impacting breeding and feeding grounds. Mitigation Strategies: Habitat Restoration: Replant native vegetation and create new habitats to compensate for lost areas. Sediment Management: Implement measures to control sediment transport and maintain water quality. Fish Passages: Design fish ladders or bypass systems to facilitate fish migration. Erosion Control: Use erosion control techniques such as silt fences, riprap, and revegetation to prevent soil erosion.

24. Safety Measures: Design Features for Safety: Structural Integrity: Ensure the spillway can withstand extreme weather events and hydraulic forces. Uplift Protection: Include features to prevent uplift pressure, such as seepage cut-off walls and drainage systems. Emergency Spillway: Design an auxiliary spillway to handle overflow during extreme flood events. Debris Management: Incorporate trash racks and other debris management systems to prevent blockages and damage. Emergency Spillway Plans: Flood Routing: Develop plans to safely route excess water during high inflow events, preventing overtopping and dam failure. Monitoring Systems: Install real-time monitoring systems for water levels and structural integrity. Emergency Response: Establish emergency response protocols, including evacuation plans and communication strategies. Regular Inspections: Conduct regular inspections and maintenance to identify and address potential issues before they escalate. By considering environmental impacts and incorporating robust safety measures, the design and operation of side channel spillways can minimize ecological disruption and enhance the overall safety of dam structures.

25. Future Trends and Innovations inside Channel Spillway Design Advancements in Design: Use of Computational Fluid Dynamics (CFD) in Design: Enhanced Flow Analysis: CFD allows for detailed simulation of water flow over spillways, improving the accuracy of hydraulic capacity assessments. Optimization: Helps optimize the design by testing various configurations and predicting potential issues like cavitation or uplift forces. Visualization: Provides clear visual representations of flow patterns, aiding in better understanding and communication among stakeholders. Innovative Materials and Construction Techniques: High-Performance Concrete: Use of fiber-reinforced and self-healing concrete to increase durability and reduce maintenance. Prefabrication: Modular and prefabricated components for quicker, more efficient construction with reduced environmental impact. Advanced Reinforcement: Use of advanced composite materials and high-strength steel for improved structural integrity and longevity. Sustainable Practices: Incorporation of Eco-Friendly Designs: Green Infrastructure: Integrating natural features like wetlands and riparian buffers to enhance biodiversity and water quality. Renewable Energy Integration: Incorporating micro-hydro power generation within spillway design to harness renewable energy. Low Impact Design: Using design practices that minimize environmental footprints, such as reduced excavation and minimal vegetation disturbance. Improved Flood Forecasting Models: Advanced Hydrological Models: Incorporating climate change projections and real-time data to enhance flood prediction accuracy. AI and Machine Learning: Utilizing artificial intelligence and machine learning to analyze vast datasets for better flood risk assessment and decision-making. Early Warning Systems: Developing comprehensive early warning systems to provide timely alerts and enable proactive flood management. By leveraging advancements in technology, materials, and sustainable practices, the future of side channel spillway design promises to be more efficient, resilient, and environmentally friendly

26. References references and sources used: Flood and Coastal Erosion Risk Management Research and Development Programme https://doi.org/10.26077/fw3r-v253 Principles of fluid mechanics by Dr. Masoud Gmeil Ahmed and Prof. K.E.Bashar https://doi.org/10.26077/fw3r-v253

27. Conclusion Summary: - Achieving critical flow in spillway design is essential for maximizing discharge capacity, ensuring flow stability, controlling energy dissipation, and simplifying the design process. By targeting critical flow conditions, engineers can create more efficient, predictable, and safe hydraulic structures. The Froude number is a crucial parameter in the design of side channel spillways. It helps in understanding the flow regime, ensuring efficient flow control, and preventing structural issues. By calculating and analyzing the Froude number, engineers can optimize the spillway design for safety and performance. -Considering the water surface profile in side channel spillways is essential for ensuring hydraulic efficiency, structural safety, and design optimization. It helps in predicting and mitigating potential issues such as erosion, scouring, and improper flow distribution, leading to a more robust and efficient spillway design. -The specific energy diagram helps in identifying the critical depth and alternate depths for given flow conditions in a trapezoidal channel Importance of Side Spillways: - Their role in dam safety and flood management.

28. Why It Is Desired to Obtain Critical Flow in Spillway Design ? Setting Critical Flow Conditions : The spillway crest can be designed to create a critical depth, ensuring that flow over the spillway is at or near the critical state. Weir Design : The crest height and shape of the weir are designed to achieve critical flow conditions at the design discharge. Energy Dissipation Basin : Hydraulic Jump Location : By ensuring critical flow at the spillway crest, the downstream energy dissipation basin can be designed to handle the hydraulic jump effectively. This controls the location of the jump, preventing erosion and protecting downstream structures.

29. Water Surface Profile inside Channel Trough The water surface profile in a side channel trough can be determined using the following equation based on the conservation of linear momentum. It assumes that motion in the channel is driven solely by the water surface fall along the channel axis, with the entire energy of flow over the crest being dissipated and not contributing to the motion along the channel. Axial velocity is generated only after incoming water particles merge with the channel stream. Equation: Variables: Δy : Drop in water surface between Section 1 and Section 2 (in meters) g: Acceleration due to gravity (in m/s^2) V1​: Velocity at Section 1 (in m/s) V2​: Velocity at Section 2 (in m/s)